The present invention relates generally to the data processing field, and more particularly, relates to a system and method for calibrating a corner frequency of a tunable filter using an ADC code difference method in a direct access storage device.
Direct access storage devices (DASDs) often incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks. Typically servo information is provided on one or more disk surfaces for reading by the transducer heads for accurately and reliably positioning transducer heads on the disk surfaces at a specific location to read and write data.
As channel speeds go faster, conventional arrangements of circuit functions can be a limiting factor in overall performance. In the design of new DASDs, the performance requirements can be more demanding than the data channel can deliver with traditional architectures.
A need exist for an effective mechanism for calibrating a corner frequency of a tunable filter, such as a continuous time filter (CTF) used in the DASD data channel. Corner frequency calibration (CFC) takes the place of fuse trims in older technologies. Corner frequency calibration leads to tremendous test and technology savings over fuse trims.
A principal object of the present invention is to provide a system and method for calibrating a corner frequency of a tunable filter using an ADC code difference method. Other important objects of the present invention are to provide such system and method for calibrating a corner frequency of a tunable filter using an ADC code difference method substantially without negative effect; and that overcome many of the disadvantages of prior art arrangements.
In brief, a system and method are provided for calibrating a corner frequency of a tunable filter using an ADC code difference method. A method for calibrating a corner frequency of a tunable filter in a direct access storage device includes generating a signal having a frequency within a pass band of the tunable filter to be passed to the tunable filter. The gain of the signal is adjusted to a first threshold level. The corner frequency of the signal is shifted to a second threshold level, whereby the corner frequency of the tunable filter is calibrated at a desired frequency.
A system for calibrating a corner frequency of a tunable filter in a direct access storage device includes calibrate control logic coupled to a tunable filter. A signal source generating a signal having a frequency within a pass band of the tunable filter to be passed to the tunable filter is coupled to the tunable filter by a variable gain amplifier. An analog-to-digital converter (ADC) is coupled to the tunable filter. The ADC produces a digitized signal in response to receiving the signal from the filter. The calibrate control logic adjusts a gain of the digitized signal to a first threshold level. The calibrate control logic shifts the corner frequency of the digitized signal to a second threshold level, whereby the corner frequency of the tunable filter is calibrated at a desired frequency.
In accordance with features of the invention, the first threshold level is set to a first ADC code and the second threshold level is set to a second ADC code. The second threshold level, second ADC code is set to the equivalent code of any given attenuation setting, for example, about 3 dB less than the first threshold level, first ADC code.